The complexities of golf club design are well-known. The choice of specifications for each component of the club (i.e., the club head, shaft, hosel, grip, and subcomponents thereof) directly impacts the performance of the club. Thus, by varying the design specifications, a golf club can be tailored to desired performance characteristics.
The design of club heads has long been studied. Among the more prominent considerations in club head design are loft, lie, face angle, horizontal face bulge, vertical face roll, face progression, sole curvature, center of gravity location, and overall head weight. While this basic set of criteria is generally the focus of golf club engineering, several other considerations must also be addressed. The interior design of the club head may be tailored to achieve particular characteristics, such as by including hosel or shaft attachment means, perimeter weighting on the face or body of the club head, and fillers within hollow club heads. The choice of materials for manufacture of the club head, must also be considered.
The type of surface treatment on the outer surface of the face is an additional design consideration. The United States Golf Association (USGA), the organization that sets the rules of golf in the United States, has instituted a rule that prohibits the competitive use in any USGA sanctioned event of a golf club where the surface roughness within an impact area of the face exceeds that of decorative sandblasting or fine milling. To spite this rule, it is widely known that many players create a roughened club head face, in order to obtain a greater backspin on their shots.
Additionally, faces are traditionally provided with stria or grooves, at regularly spaced intervals on the surface. The grooves are usually parallel, and must conform to standards established by the USGA covering groove cross-sectional symmetry, groove edge roundness, distance between adjacent grooves, and groove depth.
Various theories have been advanced to either explain or dismiss the importance and influence of grooves. The physical influence of the groove on ball trajectory, for example, may be partly attributed to the momentary deformation of the golf ball cover into the groove upon impact. This deformation is dictated by the modulus of elasticity of the golf ball cover material. Grooves are generally credited with providing large-scale, or macro-roughening on the club head face, thereby increasing back spin. Grooves in the club face may also assist a player in club alignment at address. While the degree of influence of club facial grooves on ball trajectory is disputed, grooves are largely recognized as a meaningful consideration in club head design.
The designs for golf club heads also must be strong enough to withstand the impact forces that occur due to contact between the head and the ball. The loading that occurs during this brief impact can confer an acceleration to the golf ball that is 20,000 times the acceleration of gravity, which is about four orders of magnitude greater than that of gravity. Thus, the club face and body should be designed to resist permanent deformations or catastrophic failure, such as by cracking.
It is not unusual for the club heads of prior art woods to have a face thickness exceeding 0.12 inch. This thickness has typically been required so that the club head face can withstand the impact forces. The faces of irons must also withstand considerable stresses, and as disclosed in U.S. Pat. No. 5,971,868 to Kosmatka. Thus, the faces of irons may be provided with a contoured back surface to provide increased structural integrity. Nevertheless, the design of hollow woods presents distinctly different challenges from irons, particularly due to the cavities defined within hollow woods. Whether produced by investment casting, molding, or otherwise, woods are subjected to different manufacturing stresses, and different performance requirements than irons.
The thickness of the club head face impacts various club head parameters, including the overall weight of the club head, the rigidity of the face, the vibration characteristics of the club head, the sound produced upon impact of the face with a ball, and the location of the center of gravity of the club head. In some club heads, it is desirable to minimize face thickness. Any decrease in thickness, however, must be compensated for by adjusting other design considerations. Such adjustments may include the provision of other structural features on the back surface of the club face, or the inner surface of the club head shell. Another optional adjustment includes the use of a filler material in the shell. Furthermore, the overall construction of the club head may be adjusted, such as by using a face plate insert that is fit to a club head shell, by welding, soldering or other means. Alternatively, the face plate insert may be integrally formed with the shell.
Particularly during casting of a club head, it is difficult to repeatedly produce the desired shape to a tight dimensional tolerance. However, the performance of a golf club head, particularly a metal wood, is in part a function of the proper shape and size of the club face. One especially vexing problem encountered during casting of prior art club heads is that the club head face, which is initially cast with a generally convex exterior surface, upon cooling often collapses inward and fails to retain the desired shape. Such a problem may be exacerbated in club heads with thin faces.
Thus, there is a need for a golf club head that can be consistently manufactured with a desired club head shape and size, and has a face that can withstand the impact stresses encountered during ball striking. More particularly, there is a need for a club head with a thin face that performs well. Additionally, there is a need for a club head that minimizes the degree of backspin imparted to a golf ball.